4. Water Consumption
Water provided for human consumption requires
treatment in order to make it
• safe (potable)
• pleasant to taste (palatable)
Modern technology offers remarkable capabilities
to accomplish these goals
• introduction of new and different pollutants
• cost of treating to required levels is a challenge
for the water supply industry
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5. Water Demand
• Municipal water supplies are treated to
be both palatable and potable,
regardless of their intended use
• If each person uses about 100 litres of
water per day
• Commercial and industrial users may
increase that demand by more than 5
times
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6. Drinking Water - Quality
Each source presents its own
Our water supply comes problems
from two sources
• Surface water has elevated
• surface waters i.e. levels of soil particles and algae,
rivers, lakes and making the water turbid
• may contain pathogens
reservoirs
• groundwater, which is • Groundwater has higher levels
of dissolved organic matter
stored below the (yellow color) and minerals such
as iron
earth's surface • Both sources may have high
levels of calcium and magnesium
(hardness)
• both can be contaminated
by toxic chemicals
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10. Conventional Surface Water
Treatment
Raw water
Screening Filtration
sludge sludge
Alum
Coagulation Cl2 Disinfection
Polymers
Flocculation Storage
Sedimentation Distribution
sludge
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11. Screening
• Removes large solids
logs
branches
rags
fish
• Simple process
may incorporate a mechanized trash removal system
• Protects pumps and pipes in Water Treatment
Plants
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12. Coagulation
• Small particles are not • In coagulation
removed efficiently by • we add a chemical such
sedimentation because they as alum which produces
settle too slowly positive charges to
• they may also pass through neutralize the negative
filters charges on the particles
• easier to remove if they are • particles can stick together
clumped together • forming larger particles
• Coagulated to form larger • more easily removed
particles, but they don't • process involves addition of
because they have a negative chemical (e.g. alum)
charge
• repel each other (like two • rapid mixing to dissolve the
north poles of a magnet) chemical
• distribute it evenly
throughout water
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13. Coagulants
• Aluminum Sulfate Factors for choosing a
Al2(SO4)3 coagulant?
• Ferrous Sulfate FeSO4 1. Easily available in all
• Ferric Sulfate dry and liquid forms
Fe2(SO4)3 2. Economical
• Ferric Chloride FeCl3 3. Effective over wide
• Lime Ca(OH)2 range of pH
4. Produces less sludges
Aluminum salts are 5. Less harmful for
cheaper but iron salts are environment
more effective over wider 6. Fast
pH range
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14. Flocculation
• Now the particles have a neutral
charge
• can stick together
• The water flows into a tank with
paddles that provide slow mixing
• bring the small particles
together to form larger
particles called flocs
• Mixing is done quite slowly and
gently in the flocculation step
• If the mixing is too fast, the
flocs will break apart into small
particles that are difficult to
remove by sedimentation or
filtration.
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15. Sedimentation
• water flows to a tank called a
sedimentation basin
• gravity causes the flocs to
settle to the bottom
• Large particles settle more
rapidly than small particles
• It would take a very long time
for all particles to settle out
and that would mean we would
need a very large sedimentation
basin.
• So the clarified water, with
most of the particles removed,
moves on to the filtration step
where the finer particles are
removed
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16. Filtration
• The filtration apparatus is a
concrete box which contains sand
(which does the filtering), gravel
(which keeps the sand from getting
out) and underdrain (where the
filtered water exits)
• After the filter is operated for a
while, the sand becomes clogged
with particles and must
be backwashed
• Flow through the filter is reversed
and the sand and particles are
suspended
• The particles are lighter than the
sand, so they rise up and are flushed
from the system. When backwashing
is complete, the sand settles down
onto the gravel, flow is reversed and
the process begins again
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17. Sedimentation Tank
Aeration
Flocculation
Coagulation
Raw water
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19. Disinfection
• With particles removed, it only
remains to
provide disinfection, so that no
pathogens remain in the water
• Protozoan pathogens are large in
size and have been removed with
other particles
• Bacteria and viruses are now
destroyed by addition of
a disinfectant
Chlorination
• Enough chlorine is added so that
some remains to go out in the
water distribution system,
protecting the public once the
water leaves the plant
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20. Softening
• Areas where water comes into
contact with limestone, there
may be high levels of calcium and
magnesium present
• these chemicals make the water
"hard"
• Hardness is removed by a
process called softening
• Two chemicals (lime, CaO and
soda ash, Na2CO3 ) are added to
water
• causing the calcium and
magnesium to form precipitates
• solid substance is then removed
with the other particles by
sedimentation and filtration
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21. Synthetic Organic Chemicals
• Water supplies can be contaminated with
synthetic organic chemicals (SOCs) from
agricultural runoff or commercial and
industrial sources
• such as the leaking underground storage
tank
• These chemicals are not efficiently
removed by the simple water treatment
process
• These chemicals can be removed by
passing the water through a layer
of activated carbon in a column
• The carbon granules strongly attract
organic chemicals removing them from
the water by a process called adsorption
• When the carbon is full and can't hold
any more chemical, it is removed from
the column, heated to burn off
contaminants and can then be re-used.
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22. Distribution
• Pumping of the clean
water produced at
the treatment plant
to the community is
called distribution
• This can be done
directly or by first
pumping the water
to reservoirs or
water storage tanks
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23. Onsite Treatment
Color, Taste and Odor
• The activated carbon
technology used in
municipal drinking water
treatment can be applied
in homes as well
• the carbon is contained in
a "household-sized"
column
• water passes through the
carbon removing organic
matter (which can cause a
yellow color) and also
compounds which cause
unpleasant taste and odor
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24. Onsite Treatment
At The Tap
• Home water treatment
systems may also be
installed at the tap
• Although the
technologies vary
somewhat among
products, they typically
include pre-filtration
• hardness and metals
removal by ion exchange
• organic matter removal
with activated carbon
• post-filtration
Water Treatment Plants 24
29. Implement A Project
Low Cost
• Water Conservation
• Water Treatment
• Wastewater Treatment
• Safe Drinking Water
for Flood Effected
People
• Rainwater Harvesting
Or
• Any Smart Idea related
to Public Health
Engineering
Water Treatment Plants 29
32. Water Supply
• Water supply in Potohar region
• Groundwater- major source
• Groundwater is supplemented with treated
surface water
• Disinfectants
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33. Sources of Drinking Water in
Rawalpindi
Two main sources of water in Rawalpindi.
Groundwater
• Groundwater with Tube wells
• located throughout the city
• 290 tube wells in WASA controlled area
• supplying approximately 28 MGD water to the residents
of Rawalpindi.
Surface water in the form of lakes
• Surface water is supplied from Khanpur Dam (14.6 MGD)
through Sangjani Water Treatment Plant
• Rawal Lake through Rawal Lake Water Filtration Plant (23
MGD).
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34. Ground- vs. Surface Water
Groundwater Surface water
• constant composition • variable composition
• high mineral content • low mineral content
• low turbidity • high turbidity
• low color • colored
• low or no D.O. • D.O. present
• high hardness • low hardness
• high Fe, Mn • taste and odor
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35. History
Initial Construction 1962-63
Capacity 14 MGD
Executing Agency WAPDA
Contractor WABAG, Germany
First Extension (7 MGD) 1975-79
Extended Capacity. 21 MGD
Executing Agency PHED, Govt. of Punjab
Contractor M/S Federal Const. Corp. Lahore.
Second Extension (7 MGD) 2000-2002
Extended Capacity. 28 MGD
Executing Agency PMU, WASA/RDA
Contractor VA TECH. WABAG GmbH,
Austria.
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36. Main Components
• Screening
• Coagulation
• Aeration
• Flocculation
• Sedimentation
• Filtration
• Disinfection or Chlorination
• Lime Dosing
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37. Components
Screening
• 3 Bar Screens.
• large pieces
• form of branches of trees
• leaves
• clothes
• plastic bags
• dead animal
Aeration
• 2 Blowers. Air flow @ 6 m3/min.
• remove taste and odor problems from incoming raw water
• Dissolved Oxygen (DO) level of water is enhanced by this process
Coagulation
• 2 geared drives
• shaft mounted mixers for alum mixing
• coagulant delivery pipes
• alum is added and rapidly mixed with water
• remove suspended particles in the form of turbidity
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38. Components
• Flocculation
• Clarifier # 1 to 3
• 3 Mechanical Flocculation mounted on a central rotating full
bridge with sludge scraper rotating bridge
• Clarifier Area = 475 m2
• Up flow velocity = 2.55 m/hr.
• Total flow = 336 L/s
• Clarifier # 4
• 4 flat bottom clarifiers Hydraulic flocculators (Vertical baffles)
16 sludge concentrator Cones
• Clarifier Area = 4 x 190 = 760 m2
• Up flow velocity = 2.2 m/hr.
• Total flow = 475 L/ s
• Coagulant is mixed through vertical baffling arrangements
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39. Components
Sedimentation
• large flocs are removed by gravity settling
• clear water is collected from the surface
• settled material (sludge) removed from sedimentation tank
• rotating vipers and sludge valves
Filtration
• removal of suspended non settleable solids from the drinking water
• supernatant water after sedimentation
• passed through a 1.4 meter column of silica sand
• effective size of 0.95mm ( 10 %)
• filtration rate of 5.4 m/hr. (average)-6.5 m/hr (Max)(110-130 glns/ft2. /hr.)
Filter Backwashing
• Conventional backwashing system includes
• Compressed air
• Air and Water
• Water
• Approximate time 12 to 20 minutes
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40. Filter Backwash
• Sand is backwashed when
• It becomes clogged
• Turbidity of filtered water gets too high
• During backwash, water is pumped upwards
through the sand bed
• Sand becomes “fluidized”, and particles are
flushed from the sand
• Dirty backwash water is pumped into a settling
pond and either
• Recycled back into plant or
• Disposed
• Backwashing can consume 1% to 5% of a plant’s
production
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41. Sedimentation Tank
Aeration
Flocculation
Coagulation
Raw water
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43. Components
Disinfection or Chlorination
• Liquid chlorine is used for this purpose
• dosage rate varies from 1.5 to 2.0 mg chlorine per
liter of water
• depending upon the level of contamination, pH, and
temperature
• ensuring the residual chlorine upto 0.3-0.5 mg/l.
Lime Dosing
• last unit process applied at Rawal Lake water
filtration plant
• lime is used to adjust the pH of water
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44. Disadvantages of Chlorination
Chlorine is a dangerous chemical because
1. it irritates the respiratory system
2. it irritates the eyes
3. can form Trihalomethanes, THMs, which are possible
carcinogens
Other disinfectant chemicals
Ozone gas (O3)
Ultraviolet light (UV)
Not as desirable because
More expensive than chlorine
Can’t maintain a residual concentration
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45. Water Quality Monitoring
Program
• Water quality analysis laboratory
• regularly monitor and analyze the quality of
water supplied through plant
• equipped with latest instruments and chemicals
• to test all the basic physico-chemical and
biological parameters
• recommended by the World Health Organization
• Urban Water Supply & Sanitation Project Phase
I
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46. Serial No. Water Quality Parameter
PHYSICAL PARAMETERS
1 Appearance
2 Color
3 Odor
4 Taste
5 Temperature
6 Turbidity
CHEMICAL PARAMETERS
7 pH
8 Alkalinity
9 Hardness as CaCO3
10 Electrical Conductivity
11 Sulphate
12 Calcium
13 Magnesium
14 Total Dissolved Solids
15 Chlorides
16 Residual Chlorine
17 Nitrate as NO3-
18 Nitrite as NO2-
BACTERIOLOGICAL PARAMETERS
19 Total Coliform Count
20 Fecal Coliform Count
TOXIC SUBSTANCES
21 +3/+5
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Arsenic as 46
22 Cyanide as CN-
47. Treated Water Quality
• Turbidity. 1-3 NTU
• Color. Colorless
• Odor Unobjectionable
• pH 7.5 to 9.5
• Residual Chlorine. 0.3 to 0.5 mg/L
(at WW 1 and Topi WW)
• Coliform Bacteria Nil/100 ml
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48. Rawal Lake Catchment Area
Poultry Waste from
Noor Pur Shahan Murree
Bari Imam
Q.A. Malpur
Chatter Park
University Village
Diplomatic
Enclave
Kurrang
River
Bani Gala
Village
Lakhwal
Village
Filtration Plant
WASA
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65. Safe Drinking Water
How can you ensure
that your drinking
water is safe?
a) Boiling
b) Storing it safely
c) Drinking water from
safe sources
d) All of above
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